1. Field of the Invention
The present invention relates to a device for automatic detection of states of motion and rest and to a portable electronic apparatus incorporating it.
2. Description of the Related Art
As is known, reduction of power consumption is one of the main objectives in any sector of modern microelectronics. In some fields, however, power consumption has an even determining importance in the evaluation the quality of a product. Many widely used electronic devices, in fact, are provided with a stand-alone battery supply and are normally disconnected from the mains supply; this is, for example, the case of cell phones and cordless phones, of palm-top computers and radio frequency pointer devices for computers (mouses and trackballs). It is clear that the reduction both of supply voltages and of currents advantageously involves an increase in the autonomy of the device and hence a greater convenience of use.
Furthermore, frequently the cited above devices are effectively used just for brief periods, whereas for most of the time in which they are on they remain inactive. Consider, for example, the ratio between the duration of a call from a cell phone and the average time between two successive calls. It is clear that, for almost the entire period of operation, the cell phone remains inactive, but is in any case supplied and thus absorbs a certain power. In effect, the autonomy of the device is heavily limited.
Some devices, after a pre-determined interval of inactivity, can be automatically set in a wait state (stand-by), in which all the functions not immediately necessary are deactivated; for example, in a cell phone it is possible to turn off the screen and all the circuitry that is not involved in identifying an incoming call.
To reactivate the devices from stand-by, it is advantageous to exploit a signal linked to an event (such as, for example, reception of a call signal, in the case of cell phones). However, since it is not always possible to associate a signal to an event (for example, in the case where it is the user who wants to make a call), normally a reactivation key is provided, that the user can press for bringing back the device into a normal operative state.
In this case, however, one drawback lies in that the device is not immediately ready for use: the user must in fact pick up the device, press the reactivation key and wait for the extinction of a transient in which the functions previously deactivated are restored. Although this transient is relatively brief (at the most in the region of one second), it is not however negligible and in some cases can render the device altogether inefficient. For example, in a radio frequency mouse, the restore time would be so long that the advantage of having low consumption in stand-by would be basically nullified by the lower efficiency of use.
It would, instead, be desirable to have available a device incorporated in an apparatus that is able to generate automatically a reactivation signal when the apparatus is to be used.